A Big O Tires Tech Explains A Few Common Car Terms ...
The master cylinder is a holding tank for brake fluid. As the brake
pedal is pushed down, the cylinder forces fluid to each of the wheels.
A worn master cylinder can become leaky causing dangerously unreliable
brakes. You should periodically check you brake fluid levels and the
master cylinder for leakage.
The only visible part of a vehicle’s braking system, the brake pedal,
is connected directly to the master cylinder. The pedal can be an indicator
of brake problems if it travels too far, feels "hard" or "soft" or pulses.
This can mean low or leaking fluids, damaged brake rotors or unevenly worn
shoes or pads.
The combination valve is comprised of a metering valve, proportioning valve,
and brake warning light. It helps regulate the amount of pressure on each
set of wheels to insure the front and rear brakes are applied appropriately
for different braking situations. Problems with the combination valve can
cause a vehicle’s wheels to lock up.
Drum Brake Assembly
A drum brake assembly is the most common method of stopping a vehicle’s
rear wheels. The master cylinder’s fluid pressure forces the wheel cylinder
to push brake shoes against the brake drums attached to the rear wheels.
The resulting friction caused by the stationery shoes against the revolving
drum is what makes the rear wheels slow to a stop. When brake shoes or
drums become worn, stopping becomes unreliable and requires excessive
pressure on the brake pedal.
The wheel cylinder is a very important part of the drum brake assembly.
It is made up of fluid activated pistons that push brake shoes against
the wheel drums to slow the vehicle. Leaking wheel cylinders are the
cause of many brake problems, such as unreliable stopping, brake shoe
damage and even partial brake system failure.
Disc Brake Assembly
Most cars use disc brakes for their front brakes because of their ability
to withstand more heat than drum brakes. Disc brakes work when fluid from
the master cylinder compresses brake pads against rotors attached to the
front wheels. The friction caused by the stationery pads meeting the
revolving rotors results in the rotors and the attached wheels slowing
to a stop. Disc brake rotors and pads are subjected to abuse and should
be checked for wear on a regular basis. Faulty disc brakes can vibrate
during braking and can fail completely.
The tilted direction of the wheels toward or away from one another when
viewed from above. Toe is generally considered the most critical tire
wear angle. Tires that "toe-in" point toward each other. Tires that
"toe-out" point away from each other.
The tilt of the wheels toward or away from one another when viewed from
the front. Wheels that tilt in toward the vehicle have "negative" camber
and those that tilt away from the vehicle have "positive" camber.
The angle of the steering axis in relation to an imaginary vertical line
through the center of the wheel when viewed from the side. "Positive"
caster is the when the vertical line is tilted back toward the rear,
while "negative" caster is when it is tilted forward. A proper caster
angle stabilizes the car for better traction.
Thrust Angle (Alignment)
The relationship of all four wheels to each other, as well as their overall
relationship to an imaginary center line running from bumper to bumper.
"Thrust line" refers to the direction in which the rear wheels are pointed.
Thrust angle is correctable on cars with adjustable rear suspensions. If a
vehicle has a non-adjustable suspension, then aligning the front wheels to
the rear wheels compensates for thrust angle.